(1) Field of the Invention
The present invention relates to a laminated photosensitive plate for electrophotography, which is improved in electrophotographic characteristics such as sensitivity and mechanical properties such as abrasion resistance, toughness and adhesion.
(2) Description of the Prior Art
Polyvinyl carbazole (often referred to as "PVK" hereinafter) is widely used as a polymer photoconductor having film-forming and bonding properties for the manufacture of photosensitive materials for electrophotography. However, PVK is defective in that the toughness and adhesion are insufficient. For example, PVK is brittle, readily, wears away while used for a long time and it apt to separate from a substrate in the form of slices.
As means for overcoming these defects of PVK, there is oridinarily adopted a method in which a polymeric binder such as a polyester resin, an epoxy resin or a polycarbonate resin is incorporated into PVK. However, these polymeric binders have no photoconductivity at all, and if such non-photoconductive binder is incorporated, a disadvantage of reduction of the sensitivity of the obtained photosensitive layer cannot be avoided. Furthermore, these polymeric binders are ordinarily poor in the compatibility with PVK, and therefore, a photosensitive layer comprising a blend of PVK and such polymeric binder is likely to have a heterogeneous structure and the resulting photosensitive layer is still insufficient in electrophotographic properties.
Furthermore, it has been known from old that a PVK type photoconductor can be used for manufacture of laminated photosensitive plates, and a typical instance of such known laminated photosensitive plate comprises a conductive substrate, a charge generating layer containing a photoconductive organic pigment, which is formed on the substrate, and a charge transporting layer of a PVK photoconductor formed on the charge generating layer. In this laminated photosensitive plate, however, the defect of a relatively short life of the photosensitive plate cannot be avoided because the PVK photoconductor layer is present on outermost surface layer of the photosensitive plate and the mechanical properties of this outermost surface layer of the PVK photoconductor are insufficient as pointed out hereinbefore.